It is well known to provide a four bar linkage, such as a parallelogram linkage, to mount a support for a keyboard or other desired art device for vertical swinging movement relative to a base, such as a desk or table top, wherein the application of a manual lifting force to the support serves to release the support for vertical swinging movement into a desired position, and the release of such force serves to lock the support in such position. Prior U.S. Patents specifically or inherently disclosing this general type of mounting mechanism including U.S. Pat. Nos. 169,382; 213,775; 274,223; 714,694; 967,877; 1,050,672; 1,139,581; 1,176,272; 3,436,046; and 5,292,097.
Further, above U.S. Pat. Nos. 274,223; 714,694; 3,436,046 and 5,292,097, disclose the use of frictional engagement on cooperating locking surfaces carried by a four bar linkage to releasably lock a support in a selected position; and above U.S. Pat. Nos. 169,382; 213,775; 967,877; 1,050,672; 1,139,581; 1,176,272; and 5,292,097 disclose use of engagement between serrations on cooperating locking surfaces carried by a four bar linkage for a like purpose.